Background Most adolescents do not achieve the recommended level of physical activity (PA) in the UK. Cultural norms – captured by ethnic identity – and social cohesion are aspects of the social environment that have the potential to influence health (behaviours). This study examines the relationships between social cohesion, ethnicity and three common types of PA in adolescents. The objectives are to test whether different types of PA have similar patterns of associations with social cohesion and ethnicity and to investigate confounding and interaction effects.

Methods We used longitudinal data from the Olympic Regeneration in East London (ORiEL) study. In 2012, 3088 adolescents aged 11–12 were recruited from 25 schools in four deprived and ethnically diverse boroughs of East London. Adolescents were followed-up in 2013 and 2014. Social cohesion was operationalised as trust in people living in the neighbourhood, measured on a four-point scale at wave 2. We grouped ethnic identities into eight categories. The outcomes were self-reported binary variables: walking to school, walking for leisure, and outdoor PA in the neighbourhood. We identified potential confounders. We fitted Generalised Estimated Equation models for each outcome, with a time trend and investigated potential interactions between the exposures and time. Final available case sample size was 4811 observations from 2157 adolescents.

Results We found evidence of associations between ethnicity and the PA outcomes. Adjustment for potential confounders (socioeconomic status, health and gender) did not attenuate the relationships. In the fully adjusted models, compared to White British, Black Africans had 1.49 higher odds of outdoor PA (95% CI 1.06–2.07), Bangladeshis had 1.42 higher odds of walking to school (95% CI 1.02–1.97) and all ethnic groups had lower odds of walking for leisure (estimated ORs varied between 0.37 and 0.71). While social cohesion was not associated with walking, there was evidence of a dose-response relationship with outdoor PA. A one-category increase in cohesion increasedthe odds of outdoor PA by 1.18 (95% CI 1.07–1.30). We found no evidence of time*exposure interaction; exposures did not predict change in PA.

Conclusion This study contributes new findings to the evidence base on the social environment and PA. The ethnic diversity of the ORiEL study and its large sample size provided sufficient power to reveal how PA behaviours are patterned by ethnic groups. Further analyses will jointly model the three PA outcomes to better capture the dependency and associations between the exposures and the outcomes.